This invention relates to a feature for television systems, which permits selective blanking of the picture and/or muting the sound at a receiver. It makes use of the captioning or text feature.
Present regulations of the Federal Communications Commission permit program related data in the ASCII code format to be inserted by television broadcasters in the vertical blanking interval for line 21, field 1 of the baseband video signal. The information can be captioning (e.g., closed captions for the deaf) or text giving supplementary program information. Television receivers are now commercially available having a circuit for detecting the line 21 data.
There are also known TV receiver circuits for blanking the picture and/or muting the sound of a received signal. Faerber at al U.S. Pat. 4,333,110 is an editing system which makes use of the absence of picture information in a video signal before a commercial to lower the sound. In Olsen et al. U.S. Pat. No. 3,673,318, a TV receiver is provided with video blanking and sound muting during channel selection tuning. These systems do not require any special signal to be inserted in the transmitted signal.
There are also pay TV systems, such as that disclosed in Sechet et al. U.S. Pat. No. 4,354,201, in which the received signal is jammed or scrambled, unless the receiver has a special key corresponding to one included in the transmitted signal as digital data. Also of interest are two-way interactive CATV systems, such as disclosed in Matsumoto et al. U.S. Pat. No. 4,245,245.